Conventionally, with TTs (Target Trackings) and ARPAs (Automatic Radar Plotting Aids) (hereinafter, referred to as the TT) of ship radars, when selecting a target to be captured and tracked from a plurality of reflective objects, positions of the objects have been obtained by a first scan, a position of the target object that is predicted to be acquired in the first scan has been calculated based on a position and velocity information of the target object obtained by a second scan performed before the first scan, and the positions of the objects obtained by the first scan have been compared with the predicted position. Here, the object obtained in the first scan which is closest to the predicted position has been selected to be the target object (Nearest Neighbor Method). In some other cases, information including size, shape, and difference in position of target candidates have been compared for every scan, and the target object has been selected based on the comparison result. Note that when a rotary antenna is used and it repeats transceiving electromagnetic waves while revolving, transception(s) for one rotation are referred to as one scan, and a single transception is referred to as one sweep.
JP2010-266292A discloses an art relating to a TT function of a radar apparatus, in which a relative velocity between a radar apparatus and an object is estimated based on a plurality of phase change amounts between two echo signals from two positions of which distances and azimuths from the radar apparatus are substantially the same, and a level of possibility of crashing into the object is obtained based on the relative velocity. By being based on the phase change amount between the sweeps of the radar, the velocity information of the object can be acquired in real time, and a TT function with higher accuracy can be achieved.
However, there have been some problems with the above-described conventional methods for selecting the target object. In radar apparatuses, different signals (e.g., signals with different intensities) are received in every scan, and therefore, radar images of the echo signals change in every scan. Therefore, with the conventional configurations and methods for comparing the information for every scan and selecting the target object based on the correlation value obtained from the comparison, there have been cases where information of the target candidate becomes unstable between scans and where, when objects with similar shapes and sizes are close to each other, an object to be the target candidate is not visibly recognized (lost) and/or a different object is tracked (swop).
Alternatively, a reception signal may be binarized with respect to a threshold of a signal level. Therefore, depending on how the threshold is set, a small object, such as a buoy or a small-sized ship, from which a signal level is low is not even recognized as one of the candidates in the selection. As for an object of which a signal level is around the threshold, a detection situation changes in every scan, and thus, the cases of lost and swop have occurred.
Furthermore, the target candidate information also becomes unstable when an object exists within a range with sea surface reflection and/or clutter. Thus, the cases of lost and swop have occurred.